Author(s): Han Zheng, Eng Keong Lua, Marcelo Pias, Timothy G Griffin
Round trip times (RTTs) play an important role in Internet measurements. In this paper, we explore some of the ways in which routing policies impact RTTs. In particular, we investigate how routing policies for both intra- and inter-domain routing can naturally give rise to violations of the triangle inequality with respect to RTTs. Triangle Inequality Violations (TIVs) might be exploited by overlay routing if an end-to-end forwarding path can be stitched together with paths routed at layer 3. However, TIVs pose a problem for Internet Coordinate Systems that attempt to associate Internet hosts with points in Euclidean space so that RTTs between hosts are accurately captured by distances between their associated points. Three points having RTTs that violate the triangle inequality cannot be embedded into Euclidean space without some level of inaccuracy. We argue that TIVs should not be treated as measurement artifacts, but rather as natural features of the Internet’s structure. In addition to explaining routing policies that give rise to TIVs, we present illustrating examples from the current Internet.